Unit runs often and for short periods of time.- Long winded- sorry

Discussion in 'Maintenance and Troubleshooting' started by Makenasmom, Nov 2, 2010.

  1. Makenasmom

    Makenasmom New Member

    So here's the scoop-

    I just built a 1900 sqft home last winter, it has a full basement and the attic is heated as well.

    We hired someone to install geo, and he figured that we required a 5ton unit based on the size of the area we are heating. I thought that he did some fancy calculations to come to this conclusion, such as a heat loss calc or something, but have found out in the last few days, this was not the case. It was a best guess, based on his last 12 installs...

    Our home is insulated with 2# closed cell foam insulation, installed by my husband and I as we are installers, and therefore, I can say with complete certainty that my house (doors/windows aside) is completely sealed.

    Here's the problem- our geothem unit runs often and for a short period of time. We have our thermostat set to 63 degrees farenheit, and one morning I sat and documented that it would run for 15mins at a time with a 10-12 min break in between.
    Now having just got a $4000 catch up bill on our power for the last year!!! :eek:S I decided to do a little more digging. I shut off all the breakers in the house except the geo, and left it at 63 degrees, in 3 hours the geo unit used 8 kwh!!! at that rate it would use 64 KWH per day, just to run the geo and at our current elec rates that's $265/mth just to heat my house, and it isn't even winter yet!!!
    So we called our installer back and he threw an amp meter on the unit and kicked the temp up and said, "yep, it's working just fine! must be that your house is leaky" I tried explaining that I think it is more complicated than that and his reply was' "Are you comfortable in the house?" yes I am- "Then the geo unit is doing what it's supposed to do! I dont know what you expect me to say, it's not a miracle"

    I don't buy it, first off, we run our fireplace in the evening, it bumps up the temp on the tstat to 72 degrees, and when we get up in the morning 9 hrs later, the temp has only dropped to 68. Also, I started trying running the temp up to 65, then dropping it back down to 63. When I do that, the geo runs for 25 mins, then does not run again for 3 hrs, it takes that 3hrs to drop 3 degrees.

    So why can't my geo &/or thermostat maintain a constant temp without running in short spurts all day long?

    I'm hoping someone might have some insight?

  2. teetech

    teetech Member Forum Leader

    A1900 sq ft well insulated home should not need a 5 ton GSHP. Oversizing will cause short run times and higher cycle rates. Thermostat issues can also add to the problem. Is this a 2 stage unit?
  3. Makenasmom

    Makenasmom New Member

    Thanks Teetech,

    That's what I was afraid you'd say... When I mentioned this to our installer, he told me that it was better that the unit run for shorter spurts so as not to wear out the unit. Yes, you read that right... I tried asking how we were ever going to pull any latent heat from the unit if the system didn't even run long enough to cycle through the ground loops, and his reply- "It's running at 24 amps, it's doing what it should..."

    Sadly enough, this man came highly recommended, and now that we are in a position that we are looking for some answers, it does not appear that he is educated enough to give anything more than factory specs, and guesses.

    I'm not entirely sure if this is a 2nd stage unit or not, all I know is that it has an emergency backup, which is constantly kicking on, so the installers answer- turn off that breaker.
  4. teetech

    teetech Member Forum Leader

    If oversized I don't know why back up would be kicking in so often, leads me to think thermostat is not set up well or lacking. Do you have a make and model # on the unit?
  5. Popoff

    Popoff Member

    I feel your pain since I'm in a similar situation! My last face to face encounter with my contractor ended with him telling me I was a difficult customer and my loosing my temper and asking him to leave.

    I turned up the thermostat this morning at 6:45 from 62* to 69*. It's now over 4 hours later and the temperature in the house has climbed to 66*. The outside temperature was 25 and now it's 35. What's going to happen when winter comes???

    Sorry for the rant but I'm totally frustrated (and cold) and needed to vent.
  6. tstolze

    tstolze Member

    From my research, with a Geo unit most suggest not to change the temperature, especially during heating season. These units have a slow recovery rate and are better maintaining a constant temperature.
  7. Popoff

    Popoff Member

  8. Makenasmom

    Makenasmom New Member

    @ Teetech- it's a Honeywell FocusPRO TH6220D1028

    Rant all you want, I start vibrating every time that darn unit kicks in!
  9. teetech

    teetech Member Forum Leader

    That's a pretty basic thermostat... 2 H / 2 C stages. There is no adjustment for the staging and it probably has a 1-2 degree fixed staging differential. That's not going to help your problem.
  10. geome

    geome Member Forum Leader

    What is the manufacturer and model number of geothermal system? What is the loop type and size?

    Make sure you don't change any of the following at this point. Writing down all of the existing thermostat setup settings and please post here. We may as well look at all the settings for something that may help you since there are only 28 settings for this thermostat. For guidance on how to do this, look for "installer setup" in the thermostat's installation guide (starting on page 6 on my PDF copy of the manual.)

    While thermostat setup changes won't magically make your system correctly sized, some changes may help your situation a bit.
  11. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    Unit does sound grossly oversized if you are this side of Fairbanks.
    I do believe your thermostat has CPH settings so that you can limit the number of cycles each hour.
    Why not get a heat loss calc for your house while we're at it?
    good luck,
  12. Makenasmom

    Makenasmom New Member

    Any suggestions will be greatly appreciated. I have found someone that will come out and do a heat loss to see just how oversized we are and then I guess we'll go from there...

    Thanks again!
  13. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    If installed correctly, this sounds like we may have a secondary problem.
    While a grossly oversized heat pump may use more electricity than something "right" sized (which is compounded by the single stage configuration). I don't know why you would run 45+ minutes out of the hour this early in the year. Did you mention outdoor temp?
    I suspect your duct work may be grossly undersized as well making it have to work very hard to deliver the heat (ergo long cycles).
    Code minimum of 6 sq in/1kbtu of return air mean you need 360ish sq inches of return. Does this jive with what you have?

    Thermostat settings make sense based on data available.

  14. Makenasmom

    Makenasmom New Member

    Thanks Joe!

    Last edited: Nov 17, 2010
  15. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    With temps below freezing I would not be suprised if a properly designed unit ran 45 minutes out of the hour. Your thermostat setting is 3 cycles/hour so it is doing just that. I think you can set your thermostat to 2 or even one if you don't mind temp swings.
    You are apparently quite north of my AO so larger size may not be as far out as we think. We need a heat loss calculation to know for sure. Mix in duct size answer and your contractor might not be completely nuts.
  16. geome

    geome Member Forum Leader

    Do you have a thermostat setup function #5 available (to control stage 1 heat CPH?) It is not shaded in the manual, so you may not have this option. The thermostat manual is confusing. Maybe another pair of eyes can see something I missed.

    Are you sure aux heat is running? Perhaps turning off the aux breaker (as your installer suggested) temporarily to rule this out would make sense. You can see if this effects your power usage. Or, do you mean that the heat pump is constantly kicking on (and not necessarily the aux heat.)

    I wasn't able to access a manual for the Mammoth system, so I can't tell if it has a 1 or 2 stage compressor.
  17. Makenasmom

    Makenasmom New Member

    @ GEOME- We did end up turning the back up heat breaker off, but the t-stat kicks on the "Aux Heat" every time I bump the temp up even a single degree.

    @ Joe- So very disapointing to hear... I'll get the heat loss done, but if it comes back that it's running the way it should, I'm thinking I might try to sell the unit and run Natural Gas into the house. We used to heat our 60 yr old home, wood chip insulation, only 300 sqft smaller, with 2- 35 yr old furnaces, for less than $180/mt. At the current rate that our geo is running, it will cost us $265/mt if the temp doesn't drop any further, and lets be realistic, winter hasn't even started :eek:. Thank you very much for your help, I guess I expected more from the unit than I should have.
  18. Makenasmom

    Makenasmom New Member

    K, so I think I just had an epiphany! So you're telling me that the unit will run 3 times an hour regardless of whether it needs to or not, because of the thermostat setting? K, so maybe I'm just old fashioned, but what ever happened to a thermostat that only runs a furnace to maintain a certain set temp? Do you know if you can still get a themostat that will only kick a unit on when it needs to boost the air temp to the selected set temp?

    Gosh I hope it's as simple as this!
  19. geome

    geome Member Forum Leader

    Ok...Try setting the thermostat to a comfortable set point and don't touch it. When the system turns on by itself (without you adjusting the temperature) (and not counting the time you set the temperature to a comfortable set point) see if the aux is on (it shouldn't be.)

    When making manual changes to some thermostats, including some Honeywells, the thermostat engages multiple stages quickly, thinking that you desire to reach your new manual set point as soon as possible. With a 3 stage system (2 stage compressor+aux), first and sceond stage of the compressor typically turn on quickly and then aux if needed (especially if you bump up the thermostat 2f+ degrees.) With a 2 stage system, it sounds like your thermostat is quickly engaging 1st stage and aux.

    Also, let me know if you can adjust setup #5 while leaving your system type as is (don't change your system type!). See if you have that option enabled and what it is currently set at. Depending on how your system runs without adjusting the thermostat (see above), adjusting #5 and #6 setting may or may not be necessary.
  20. geome

    geome Member Forum Leader

    I believe the 3 CPH you listed for setup #9 is for cooling, not heating. Setup #5 should be for 1st stage heating.

    No, If you have 3 CPH selected (I'm not sure that you do) your system should not turn on 3 times per hour regardless of the need. The CPH setting is a maximum. So, if your thermostat calls for heat 1 time per hour to maintain the set point, your system will run 1 time per hour, even if you have 3 CPH selected. The system will run until the thermostat is satisfied.

    If your thermostat calls for heat 3 times per hour to maintain the set point, your system will run 3 times per hour. Ok, so what happens next?

    If your system needs to run 4 or more times per hour to maintain the set point, your compressor will run 3 times per hour and then no more until the hour is up. So, either your aux heat will engage, or your indoor temperature will drop until the hour is up (I am not sure which.)

    Decreasing CPH lengthens system run time and increases the temperature swing in the house. Increasing CHP shortens system run time and decreases the temperature swing in the house. I like to set our system at the lowest CPH that we are comfortable with. I feel this increases system run efficiency (assuming aux does not need to fill a void when CPH has been used up for the hour) and hopefully makes the unit last longer due to less start/stop cycles.

    In your case, I believe just leaving the thermostat alone will keep aux from engaging until your outdoor design point is close to being reached (assuming your system was designed, installed, operating correctly, etc.) It would be great if you can confirm that your compressor is 1 stage for heat and cooling.

    If you need to set back a few degrees to be comfortable at night, and want to keep the same thermostat, you could consider turning off the aux breaker as your installer suggested. The aux light on the thermostat may still light even though the breaker is off. THE DOWNSIDE to doing this is that you will need to turn on the breaker when your system can't keep up or the house temperature will begin to drop. ALSO, your emergency electric heat will not engage, in the event of a system lockout, until the breaker is turned on. I would not leave the breaker off if you are not home. Better to go with fewer blankets at night and get accustomed to a constant set point.

    However, there are other thermostats out there that have time/temperature droop settings that may work with your system and prevent aux from engaging prematurely. Dewayne, is it you that uses one of these?
    Last edited: Nov 17, 2010

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